This invention relates to a flexbeam for rotor blades of a helicopter and a method for the fabrication thereof and, more particularly, to a flexbeam of a hub structure provided with no bearing means and its fabrication method.
A helicopter rotor usually has a plurality of rotor blades, typically four in a cruciform shape, wherein the opposed blades are supported by flexible beams or flexbeam to be rotatable about the axis of rotation of a rotor mast. The flexbeam reacts against the centrifugal force between opposite blades and may terminate at a convenient radial position.
The flexbeam is generally classified into two types. One has a hub structure provided with bearing means, and the other has a hub structure provided with no bearing means. The flexbeam having the hub structure but no bearing means, for supporting the rotor blades of the helicopter, comprises a flapping flexible structure disposed at the central portion of the rotor blades in a cruciform configuration, as an example, and an flexible structure extending outwardly from the flapping flexible structure and including a part subjected to feathering and lead-lag motion, which is called a feathering and lead-lag motion part.
U.S. Pat. No. 4,427,340 to Metzger et al discloses a flexbeam of the type described above having an flexible structure in which a plurality of parallel ribs extend in the longitudinal direction of the rotor blade of the helicopter and are located in predetermined planes of rotation with spaces therebetween, with a total of eight upper and lower ribs being provided. The ribs thus arranged constitute a reinforced composite integral rib structure, which allows the flexbeam to be easily twisted, and an imaginary hinge portion for the flexbeam is formed for reducing the lead-lag rigidity.
Japanese Patent Laid-open Publication (Kokai) No. 55-145811 published Nov. 13, 1980 also discloses a flexbeam which is formed of a fiber composite material having a T-shape or cruciform cross-sectional shape, and in which some members and parts of the composite fiber material as well as joining portions thereof are formed with slits so as to allow the flexbeam to be readily twisted.
The structures of the flexbeams disclosed in the prior art references cited above, however, involve problems about weight reduction thereof as well as the productivity or manufacturing cost thereof.